Document potential data loss for BaseLogEntry migration in 3.0

docs/releases/3.0.md

@@ -238,6 +238,39 @@ The `content_json` field in the `PageRevision` model has been renamed to `conten
 
 The `data_json` field in the `BaseLogEntry` model (and its subclasses `PageLogEntry` and `ModelLogEntry`) has been renamed to `data`, and this field now internally uses `JSONField` instead of `TextField`. If you have a large number of objects for these models, running the migrations might take a while.
 
+If you have models that are subclasses of `BaseLogEntry` in your project, be careful when generating new migrations for these models. As the field is changed and renamed at the same time, Django's `makemigrations` command will generate `RemoveField` and `AddField` operations instead of `AlterField` and `RenameField`. To avoid data loss, make sure to adjust the migrations accordingly. For example with a model named `MyCustomLogEntry`, change the following operations:
+
+```python
+operations = [
+    migrations.RemoveField(
+        model_name='mycustomlogentry',
+        name='data_json',
+    ),
+    migrations.AddField(
+        model_name='mycustomlogentry',
+        name='data',
+        field=models.JSONField(blank=True, default=dict),
+    ),
+]
+```
+
+to the following operations:
+
+```python
+operations = [
+    migrations.AlterField(
+        model_name="mycustomlogentry",
+        name="data_json",
+        field=models.JSONField(blank=True, default=dict),
+    ),
+    migrations.RenameField(
+        model_name="mycustomlogentry",
+        old_name="data_json",
+        new_name="data",
+    ),
+]
+```
+
 ### Replaced `form_data` `TextField` with `JSONField` in `AbstractFormSubmission`
 
 The `form_data` field in the `AbstractFormSubmission` model (and its subclasses `FormSubmission`) has been converted to `JSONField` instead of `TextField`. If you have customisations that programmatically add form submissions you will need to ensure that the `form_data` that is output is no longer a JSON string but instead a serialisable Python object. When interacting with the `form_data` you will now receive a Python object and not a string.